1. Field of the Invention
The present invention relates to a method for producing L-tryptophan by fermentation, and particularly relates to a method for producing L-tryptophan with a microorganism of the genus Bacillus constructed by a gene splicing technique.
2. Description of the Prior Art
There have been two processes for the production of L-tryptophan by microbiological process: one is an enzymological process using indole and serine (or pyruvic acid and ammonia) as the starting materials and another is a ferementation process using carbohydrate as the carbon source, in which anthranilic acid or indole is sometimes used as an additional carbon source. The present invention concerns the latter fermentation process.
Examples of known microorganisms which produce L-tryptophan from carbohydrate through a fermentation process are a mutant of the genus Brevibacterium resistant to 5-methyltryptophan (U.S. Pat. No. 3,700,539), a mutant of Corynebacterium resistant to tryptophan-analog and phenylalanine-analog and requiring phenylalanine and tyrosine for growth (U.S. Pat. No. 3,849,251), a mutant of Bacillus resistant to 5-fluorotryptophan and requiring arginine, phenylalanine, lysine, leucine, or purine for growth (Japanese Published Examined patent application No. 39517/1978), a mutant of Bacillus resistant to 5-fluorotryptophan (Japanese Published Unexamined patent application No. 148093/1976), and a mutant of Enterobacter (Japanese Published Unexamined patent application No. 57888/1976).
Examples of known microorganisms which produce L-tryptophan from carbohydrate and anthranilic acid through a fermentation process are a wild strain of Aerobacter, Arthrobacter, Bacillus, Brevibacterium, Staphylococcus, Corynebacterium, Flavobacterium, Pseudomonas, Proteus, Serratia, Sarcina, Streptococcus, Xanthomonas, Candida, Saccharamyces, Zygosaccharomyces or Penicillium (Japanese Published Examined patent application No. 20711/1968), a mutant of Bacillus resistant to anthranilic acid and requiring anthranilic acid for growth (Japanese Published Examined patent application No. 29584/1972), a wild strain of Escherichia (French Pat. No. 1,207,437) and a mutant of Bacillus resistant to 5-methyltryptophan (British Pat. No. 1,298,499).
Examples of known microorganisms which produce L-tryptophan from carbohydrate and indole through a fermentation process are a wild strain of Candida (British Pat. No. 1,222,904), a mutant of Escherichia requiring anthranilic acid (U.S. Pat. No. 3,293,141), and a wild strain of Bacillus (U.S. Pat. No. 3,700,558).
Other examples of known microorganisms which produce L-tryptophan from carbohydrate are those which were constructed by gene splicing technique and are Escherichia coli strains having recombinant plasmid DNA disclosed in Japanese Published Unexamined patent applications No. 71397/1982 and No. 80398/1982, and Appl. Environ. Microbiol.,38, (2), 181-190, (1979).
However, it has been difficult to apply the known methods to commercial production of L-tryptophan because of the rather low L-tryptophan productivity of the known microorganisms.
A need therefore continues to exist for development of a novel process for production of L-tryptophan in high yields.